One of my choices has already accepted me and is waiting for my confirmation. The problem is that the confirmation deadline comes before the announcement date of the other schools I applied to. If any of those other schools accept me, I would choose them over this school. What do applicants usually do in this scenario - is it acceptable to send the confirmation but then just withdraw if I get accepted in the others?
most likely you'll have to pay a deposit at the school you've been accepted to before you hear from the other one. I think most people handle this by preparing to eat the deposit if they get into their preferred school.